Orchard sanitation fends off drosophila, researchers say

Dan Wheat/Capital Press
Petri dishes hold dead spotted wing drosophila at the Washington State University Tree Fruit Research and Extension Center in Wenatchee. Researchers say cleaning orchards after harvest may help curb the spread of the pest.

However, Oregon State University entomologist Amy Dreves has found the fly also lays eggs and survives in blueberries that have dropped and begun decaying.

For farmers, even one spotted wing drosophila fly is considered too many, as the pest can multiply rapidly, Dreves said during the recent Pacific Northwest Insect Management Conference in Portland, Ore.

Larvae that develop in fallen fruit can reach adulthood and perpetuate another generation of flies, so cleaner fields are associated with lower numbers of the spotted wing drosophila, she said.

Leftover hanging fruit can also provide habitat for the pest, which can then invade newly ripening varieties — a particular concern for organic growers with more limited crop protection options.

Even so, it’s unclear how to inexpensively remove such infested fruit and many farmers see sanitation as providing a lower return on investment compared to chemicals, Dreves said.

Sanitation nonetheless warrants study because the pest may eventually be able to withstand current pesticides, she said. “I feel like we’re on the road to resistance.”

Sanitation is more of a concern in greenhouse fruit production, where harvest is more continuous and fallen berries cause re-contamination, said Tom Peerbolt, research coordinator for the Oregon Raspberry and Blackberry Commission.

Farmers feared that fallen fruit would be a much bigger concern in fields when spotted wing drosophila appeared in Oregon in 2009, he said.

Since then, though, growers have been able to keep the pest controlled with chemicals and sanitation hasn’t developed into a major practical problem, Peerbolt said.

Removing such fruit isn’t economically feasible in outdoor systems, he said. “The labor cost of this is just amazing.”